I purchased an Onsrud 57-280 1/4" down cut bit for cutting 1/2" plywood. When I was using in Vcarve pro at my maker space, the tool library had an Onsrud 57-910. I looked on Onsrud's website and it says the 57-910 is heavy duty, but I didn't find any additional info about it. I'd like to know the difference between these two bits.